BLACKSBURG, Va. - In the dark of night and only two days after the carnage at Virginia Tech, Katelynn L. Johnson was counting rocks.

29, 30, 31.

"I got 32," the 27-year-old senior recalled Wednesday. "I just lost it. I broke down. I was seething. I remember saying . . . 'How could people be so mean?' "

Jim Keane, her boyfriend of five years, then asked a question, thinking he knew her answer. "Do you want to get a 33d stone?"

"Yes."

Johnson revealed the story for the first time Wednesday, solving the week-old mystery of the memorial to Seung-Hui Cho, the man responsible for the worst mass shooting in modern American history. The stone, slid into a ring of memorials at the edge of the Drillfield, drew criticism from people who find it unthinkable to honor a killer's memory beside his 32 victims.

In recent days, the stone was removed as anonymously as it was placed.

"To see this community turn on one of its own no matter what he did is heartbreaking to me," Johnson said. "If we're a community, we're a community. If we're a family, we're a family. You can't pick and choose your family."

Johnson, a Minnesota native majoring in sociology and psychology, and Keane took the rock to the Drillfield at 4 a.m. last Thursday to remain anonymous, she said.

They stayed under wraps until Johnson outed herself with a letter to Collegiate Times, the student newspaper. Johnson e-mailed the letter after reading Tuesday that someone had removed Cho's stone.

"We lost 33 Hokies that day, not 32," she wrote. "Who am I to judge who has value and who doesn't? I am not in that position. Are you?"

Someone disagreed.

After news stories about the memorial ran, the stone was gone by Monday morning.

Johnson was furious. She returned to the Drillfield, and the stone she and Keane placed was still there. If someone removed one, it was the wrong one, she said. She speculated there might have been confusion because officials had removed the name tags from memorials earlier this week to shield them from the rain.

Either way, there were 33 stones Wednesday. His name is nowhere to be seen, but a rock and dying flowers mark his place on the last stone to the left.

The letters at Cho's memorial have been preserved along with all of the items left in front of the memorials, said Mark Owczarski, a Virginia Tech spokesman.

Hokies United, a student group, set up the memorials, and the university wants to preserve the letters, cards and flowers left behind. The school has been in touch with the Library of Congress to do that.

"There's so many expressions of grief," he said. "And all of them are accepted and not judged."

Not everyone shares the university's position. Onlookers have often paused at Cho's stone, some whispering and shaking their heads about whether a killer merits such compassion.

Johnson will attend graduate school at Tech and then plans to earn a doctorate in forensic psychology. Her senior thesis was on mental illness and higher education. The 2005 school shooting in Red Lake, Minn., that claimed 10 lives, including the gunman, happened not far from her hometown.

Johnson said the media have given little insight into mental illness as a factor in Cho's rampage. If Cho was mentally ill, she said, the condition deserves her understanding. If he wasn't, Cho still deserves her respect as someone's son.

"Some people will never make that connection," Johnson said. "I understand that."